Melt the butter in a medium skillet and add the mushrooms. Cook for 5 minutes and add the minced garlic. Cook until mushrooms are browned, stirring occasionally so the garlic doesn’t burn. Remove from heat.
To assemble crostini:
Place a heaping tablespoon of the mushroom mixture on a slice of french bread. Top with 1 teaspoon of crumbled blue cheese. Sprinkle 1/2 teaspoon each of grated parmesan and fresh thyme leaves on top. Serve warm or room temperature.